The present invention relates to a semiconductor device and method for manufacturing the same; and more particularly to such device, and method such for manufacturing the same, which has a highly reliable wiring in a contact hole portion.
With a trend toward higher density of integration of a semiconductor integrated circuit, connecting portions of a wiring (such as a connecting portion between a wiring and a semiconductor substrate, a connecting portion between an upper layer wiring and a lower layer wiring, etc.) formed for connection between elements and the like are extremely reduced in dimension.
The above-described connection is made through a contact hole formed in an insulating film, but a ratio of a depth to a diameter (or a narrower width) of a contact hole (hereinafter referred to as "aspect ratio") also gradually increases with higher density of integration.
As a result, there occurs a tendency in that a defective connection is liable to occur to deteriorate the reliability of the wiring.
A proposal has been made to provide a dual layer construction of a wiring in order to prevent the reliability from being deteriorated as described above.
FIG. 1a shows one example of such proposal, in which a wiring of a dual layer construction comprising a first wiring layer 12 and a second wiring layer 13 is shown (C. Y. Ting, J. Vac. Sci. Technol., 21 (1) 1982, P14-P18).
The first wiring layer 12, of transition metal W or Mo, or alloys or compounds thereof such as TiW or TiN, is provided to prevent occurrence of reaction between the second wiring layer 13, formed of alloy containing Al as a main component, and a substrate 10 within a contact hole 14.
However, since the first and second wiring layers 12, 13 are formed by vacuum evaporation or sputtering, the wiring layer 12 is extremely thin in a bottom end portion A of a contact hole 14 formed in an insulating film 11.
The degree of such thinness is affected by the aspect ratio of the contact hole 14, the method of forming the first wiring layer 12, and the and film thickness thereof. For example, where the aspect ratio of the contact hole is 1, a step coverge factor (a ratio of film thickness between a thick portion of a wiring layer and a thin portion thereof in the contact hole) is 0.1 to 0.5.
If in the end portion A, the thickness of the first wiring layer 12 is reduced as described above, the effect of preventing the reaction between the second wiring layer 13 and the substrate 10 is lowered and the reliability of the wiring is lowered.
Further, not only the thickness of the first wiring layer 12 but the thickness of the second wiring layer 13 becomes thin in the end portion A for the same reason as described above, and therefore, current capacity of wiring (maximum current amount that may be applied to the wiring) is also lowered.
To solve the problem noted above, a method has been proposed wherein a first wiring layer 12' is formed interiorly of a contact hole 14 by selective chemical vapor deposition (hereinafter referred to as "selective CVD"), as shown in FIG. 1b, (C. E. Miller, Solid State Technol., December 1982, 85).
According to this method, the first wiring layer 12' of transition metal such as W, Mo, etc. is selectively formed within the contact hole, so as to be embedded in the contact hole 14, after which a second wiring layer 13' is formed by sputtering or the like.
As clearly shown in FIG. 1b, the first wiring layer 12' is almost completely embedded in the contact hole 14, and therefore, the step coverage of the second wiring layer 13' and current capacity are improved over those shown in FIG. 1a.
However, as shown in FIG. 1b, since the side of the first wiring layer 12' formed by the selective CVD and the side of the insulating film 11 are not in close contact with each other but there is a gap therebetween, the thickness of the first wiring layer 12' becomes thin in the end portion A' similarly to the case shown in FIG. 1a, and the effect of preventing the reaction between the second wiring layer 13' and the substrate 10 is lowered, thus making it difficult to obtain a good wiring. Furthermore, three of the present inventors have proposed a method wherein a contact hole is filled with a first metal and thereafter a second metal layer is formed (see Japanese Patent Laid-Open No. 152192/82). However, it has been desired to develop a simpler and more practical method.